It is known to digitize analog signals such as a color video signal and an audio signal and to record the resulting digital signals on a magnetic recording medium such as a magnetic tape. Typically, the digital signals are recorded in the form of data blocks of a predetermined length, and with a synchronizing signal at the beginning of each block, so that the synchronizing signals are recorded at regular intervals on the record medium. The data blocks are sometimes referred to as "sync blocks".
Each sync block includes data that represents the address of the block and the type of information recorded in the block so that the signal can be correctly processed during reproduction. The data may include, for instance, an identification of the type of information as a video or audio signal and, in the case of a video signal, may indicate the screen position of the signal information contained in the sync block. This identifying data concerning the address and information type are generically referred to as an "ID signal".
If an error occurs in the ID signal during recording or reproduction, such an error can significantly disrupt the reproduction of the recorded signal. Moreover, unlike the video and audio signals, the ID signal does not have temporal and spatial correlation, so that errors in the ID signal cannot be readily corrected by interpolation.
It is known to add a parity byte to the ID signal in order to permit error detection upon reproduction. Since error correction is also desirable, it has been proposed to encode the ID signal with an error correction code. In error correction codes, such as the Reed-Solomon code, at least two parity symbols are required. Accordingly, it has been proposed to add two parity bytes (8 bits each) to the ID signal. But since the ID signal itself usually consists of only a few bytes, this proposal results in increased redundancy in the data to be recorded.